Fluid catalytic cracking process with substantially complete combustion of carbon monoxide during regeneration of catalyst

ABSTRACT

An improved fluid catalytic cracking process providing improved product yield and selectivity employs a regenerated hydrocarbon conversion catalyst having improved activity and a low level of residual coke, desirably less than 0.05 wt. % on catalyst, obtained by burning coke from spent catalyst under balanced conditions supporting substantially complete combustion of carbon monoxide with provision for recovery of evolved heat by transfer directly to the catalyst particles particularly within a dilutephase zone in the regenerator vessel. Effluent gas from the regenerator may be discharged directly to the atmosphere with no discernible effect upon ambient air quality.

United States Patent Horecky, Jr. et al.

[ 51 Sept. 30, 1975 FLUID CATALYTIC CRACKING PROCESS WITH SUBSTANTIALLYCOMPLETE COMBUSTION OF CARBON MONOXIDE DURING REGENERATION OF CATALYSTAssignee: Standard Oil Company, Chicago, 111.

Filed: May 22, 1974 Appl. No; 472,111

Related U.S. Application Data Continuation of Ser. No. 262,049, June 12,1972, abandoned, which is a continuation-in-part of Serl No, 203,396,Nov. 30, 1971, abandoned.

2,884,303 4/1959 Metl'ailer 252/417 2,981,676 4/1961 Adams et al...208/120 2,985,584 5/1961 Rabo et a1. 208/120 3,004,926 10/1961Goering 1. 252/417 3,039,953 6/1962 Eng 08/1 0 3,351,548 ll/l967 Payneet a1. 08/120 3,513,087 5/1970 Smith 208/159 3,563,911 2/1971 Pfeiffer(it all 252/417 3,661,800 5/1972 Pfeiffer et a1. 252/417 3.838,0369/1974 Stine et a1 208/164 3,844,973 10/1974 Stine et a1 208/164 PrimaryExaminer-Delbert E. Gantz Assistant E.\aminer.lames W. HellwegeAttorney, Agent, or FirmMorton, Bernard, Brown, Roberts and Sutherland[57] ABSTRACT An improved fluid catalytic cracking process providingimproved product yield and selectivity employs a regenerated hydrocarbonconversion catalyst having [52] U.S. Cl. 208/120; 252/417; 208/164improved activity and a low level of residual coke, de- [51] Int. Cl.C10G 11/18, B01] 29/38 bl 1 mi 005 t 7 c til t ht" d b [58] Field ofSearch 252/417, 419; 208/120, 655 a 3 208/164 burning coke from spentcatalyst under balanced con ditions supporting substantially completecombustion of carbon monoxide with provision for recovery of [56]References Cited evolved heat by transfer directly to the catalystparti- UNITED STATES PATENTS cles particularly within a dilute-phasezone in the re- 2,382,382 8/1945 Carlsmith et a1. 252/417 generatorvessel, Effluent gas from the rcgcncrator 2398739 4/1946 Greensfclder---252/417 may be discharged directly to the atmosphere with no 2,398,759Al'lgfill discernible effect p ambient air 2,414,002 1/1947 Thomas eta1. 252/4l7 2,425,849 8/1947 Voorhees 252/242 29 Claims, 3 DrawingFigures Upper Sac/Ion 23 37 Laws! 1 Section l3 12 a i 4i 5 I ,l/ a

.L/ T l US. Patent Sept. 30,1975 Sheet 1 of 3 3,909,392

US. Patent Sept. 30,1975 Sheet 2 of 3 3,909,392

Upper Section IL;

Fig. 3

CARBON ON REGENERATED CATALYST FLUID CATALYTIC CRACKING PROCESS WITHSUBSTANTIALLY COMPLETE COMBUSTION OF CARBON MONOXIDE DURING REGENERATIONOF CATALYST This application is a continuation of application Ser. No.262,049, filed June 12, 1972, now abandoned which in turn is acontinuation-in-part of application Ser. No. 203,396, filed Nov. 30,1971, now abandoned.

BACKGROUND OF THE INVENTION Catalytic cracking of heavy petroleumfractions is one of the major refining operations employed in theconversion of crude petroleum oils to desirable fuel products such ashigh-octane gasoline fuels used in spark-ignited internal combustionengines. Illustrative of fluid catalytic conversion processes is thefluid catalytic cracking process wherein suitably preheated highmolecular weight hydrocarbon liquids and vapors are contacted with hot,finely-divided, solid catalyst particles, either in a fluidized bedreactor or in an elongated riser reactor, and maintained at an elevatedtemperature in a fluidized or dispersed state for a period of timesufficient to effect the desired degree of cracking to lower molecularweight hydrocarbons typically present in motor gasolines and distillatefuels. Suitable hydrocarbon feeds boil generally within the range fromabout 400 to about 1200F. and are usually cracked at temperaturesranging from 850 to 1050F.

In a catalytic process some non-volatile carbonaceous material, or coke,is deposited on the catalyst particles. Coke comprises highly condensedaromatic hydrocarbons which generally contain 4-10 wt. hydrogen. As cokebuilds up on the catalyst, the activity of the catalyst for cracking andthe selectivity of the catalyst for producing gasoline blending stockdiminish. The catalyst particles may recover a major proportion of theiroriginal capabilities by removal of most of the coke therefrom by asuitable regeneration process.

Catalyst regeneration is accomplished by burning the coke deposits fromthe catalyst surface with an oxygencontaining gas, such as air. Manyregeneration tech niques are practiced commercially whereby asignificant restoration of catalyst activity is achieved in response tothe degree of coke removal. As cokeis progressively removed from thecatalyst, removal of the remaining coke becomes most difficult and, inpractice, an intermediate level of restored catalyst activity isaccepted as an economic compromise.

The burning of coke deposits from the catalyst requires a large volumeof oxygen or air. Oxidation of coke may be characterized in a simplifiedmanner as the oxidation of carbon and represented by the followingchemical equations:

C. O26 Reactions (a) and (b) both occur typical catalyst regenerationconditions wherein the catalyst temperature may range from about 1050 toabout 1300F. and are exemplary of gas-solid chemical interactions whenregenerating catalyst at temperatures within this range. The effect ofany increase in temperature is reflected in an increased rate ofcombustion of carbon and a more complete removal of carbon, or coke,from the catalyst particles. As the increased rate of combustion isaccompanied by an increased evolution of heat, whenever sufficientoxygen is present, the gas-phase reaction (c) may occur. This latterreaction is initiated and propagated by free radicals.

A major problem often encountered and sought to be avoided in thepractice particularly of fluid catalyst regeneration is the phenomenonknown as afterburning, described, for example, in Hengstebeck, PetroleumProcessing, McGraw-Hill Book Co., 1959, at pages and and discussed inOil and Gas Journal, volume 53 (no. 3), 1955, at pages 93-94. This termis descriptive of the further combustion of CO to CO as represented byreaction (0) above, which is highly exothermic. After burning has beenvigorously avoided in catalyst regeneration processes because it couldlead to very high temperatures both damaging to equipment and believedto cause permanent deactivation of catalyst particles. All fluidcatalyst regenerator operators have experienced afterburning and, withtheir ingenuity, a very substantial body of art has developed aroundnumerous means for controlling regeneration techniques so as to avoidafterburning. More recently, as operators have sought to raiseregenerator temperatures for various reasons, elaborate arrangementshave also been developed for control of regenerator temperatures at thepoint of incipient afterburnin g by suitable means for control of theoxygen supply to the regenerator vessel as set forth, for example, inU.S. Pat. Nos. 3,161,583 and 3,206,393 as well as in U.S. Pat. No.3,513,087. In typical contemporary practice, accordingly, with avoidanceof afterburning, the flue gas from catalyst regenerators usuallycontains very little oxygen and a substantial quantity of CO and CO2 innearly equimolar amounts.

Further combustion of CO to CO is an attractive source of heat energybecause reaction (c) is highly exothermic. Afterburning can proceed attemperatures above about 1 100F. and liberates approximately 4350 BTU/lb. CO oxidized. This typically represents about one-fourth of the totalheat evolution realizable by complete combustion of coke. The combustionof CO can be performed controllably in a separate zone, or CO boiler,after separation of effluent gas from catalyst, as described in, forexample, U.S. Pat. No. 2,753,925, with the released heat energy beingemployed in various refinery operations such as the generation of highpressure steam. Other uses of such heat energy have been described inU.S. Pat. Nos. 3,012,962 and 3,137,133 (turbine drive) and U.S. Pat. No.3,363,993 (preheating of petroleum feedstock). Such heat recoveryprocesses require separate and elaborate equipment but do serve tominimize the discharge of CO into the atmosphere as a component ofeffluent gases. This serves to avoid a potentially serious pollutionhazard.

Silica-alumina catalysts, employed conventionally for many years invarious processes for the cracking of petroleum hydrocarbons, are notparticularly sensitive to the level of residual coke on catalystprovided that the coke level be no greater than about 0.5 wt. However,silica-alumina catalysts have largely been supplanted by catalystsadditionally incorporating a crystalline aluminosilicate component andknown as zeclites or molecular sieves. The molecular sievecontainingcatalysts are much more sensitive to the residual coke level, beinggreatly affected both with regard to catalyst activity and to catalystselectivity for conversion of feed to the desired product or products.Due to the difficulties encountered in conventional catalystregeneration techniques as set forth above for removal of the lastincrements of residual carbon, the practical coke level usuallycorresponds to a residual coke content on regenerated catalyst withinthe range from about 0.2 to about 0.3 wt.

Enhanced activity and selectivity are achievable with sieve-typecracking catalysts at low coke levels, providing an attractive incentivefor discovering a means for reducing residual coke levels still further.Coke levels below 0.05 wt. are greatly to be desired but usually cannotbe achieved by commercially practicable means. The need for such thingsas larger regeneration vessels and greater catalyst -inventory togetherwith greater heat losses and the like all serve to discourage attainmentof ideal equilibrium catalyst activity levels.

SUMMARY OF THE INVENTION This invention relates to an improved fluidcatalytic cracking process, including an improved process for theregeneration of catalysts employed in fluid catalytic conversion ofpetroleum feedstocks wherein the catalyst is deactivated by thedeposition of coke on the catalytic surfaces. A practical method for theregeneration of conversion catalysts, particularly fluid crackingcatalysts, has now been discovered and is sustainable over a long periodof operation, enabling the coke level on regenerated catalyst to bemaintained at an extremely low level while simultaneously maintaining afavorable heat balance in the conversion unit and providing a flue gasstream having an extremely low carbon monoxide content.

In a preferred embodiment of the invention, the combustion of carbonmonoxide to carbon dioxide is carried substantially to completion withinthe regeneration vessel in a subsequent and usually relatively dilutesecondary catalyst regeneration zone advantageously at a temperaturebetween about 1200 and l500F., desirably between about I250 and I450F.Partially regenerated catalyst from a relatively dense primary catalystregeneration zone can be controllably flowed through the secondary zonein an amount and at a rate sufficient to absorb substantially all of theheat released by the combustion occurring in the secondary zone.Although most of the coke is burned from the catalyst in the primaryzone, additional coke is burned from the partially regenerated catalystwhile present in the secondary zone and catalyst substantially free ofcoke may be recovered for recycle to the hydrocarbon conversion zone.Heat from the combustion of carbon monoxide absorbed by the regeneratedcatalyst provides part of the process heat required in the conversionzone. Additionally, the flue-gas stream released from the secondaryregeneration zone is substantially free of carbon monoxide.

In another embodiment of the invention substantially all of thecombustion, including both the oxidation of coke or carbon and theoxidation of carbon monoxide, occurs within a single relativelydensephase regeneration zone in response to the proper control ofprincipally the regeneration temperature and gas velocity.

An outstanding advantage of this invention lies in providing aregenerated catalyst generally possessing enhanced activity andselectivity characteristics more closely approaching those of freshconversion catalyst particularly for use in conversions effected at veryshort contact times in riser reactors. Accordingly, higher conversionsof feedstock and higher yields of desirable conversion products may beachieved. The controllably balanced conservation of heat additionallyprovides an effective heat reservoir without requiring a largeproportion of catalyst relative to oil in the fluidized conversion zoneor the retention of a large quantity of catalyst in the regenerationvessel.

The carbon monoxide content of the flud gas from this novel regenerationprocess can be maintained at less than about 0.2 vol. for example, about500l000 ppm. Advantageously, the content is even lower, for example,wihthin the range from 0 to 500 ppm. This low concentration of carbonmonoxide in the flue-gas stream permits the direct release of effluentgases to the atmosphere while meeting ambient air quality standards.This advantage of the invention additionally permits the elimination ofcapital expenditures otherwise required for installation ofCO boilersand associated turbine-type devices or other means for partial recoveryof energy.

The novel regeneration process of this invention is advantageouspracticed as a key step in the fluid catalytic cracking process where atleast a substantial portion of the conversion is effected in adilute-phase transfer line or riser reactor system requiring very activecatalysts employed at relatively high space velocities. Catalystregenerated by the process of this invention desirably contains lessthan 0.5 wt. coke and advantageously no more than about 0.01 wt. coke.This extremely low coke level is especially preferred when employingfluid cracking catalysts containing crystalline aluminosilicates,otherwise known as zeolites or molecular sieves. The cracking activityof sievecontaining catalysts and their selectivity for converting feedto desired products are both dramatically affected in a favorabledirection by the increased elimination of residual carbon or coke duringregeneration.

DESCRIPTION OF THE DRAWINGS The attached drawings,

FIGS. 1 and 2, provide elevational views, partly in section, ofembodiments of apparatus suitable for catalyst regeneration according tothe process of this invention.

The chart presented in FIG. 3 illustrates the beneficial effectsrelative to conversion and yield achieved by diminishing the carbon, orcoke, content of regener ated fluid cracking catalyst to the unusuallylow levels mentioned previously.

DETAILED DESCRIPTION OF THE INVENTION The process of this inventionprovides a regenerated conversion catalyst having a very low cokecontent, desirably less than 0.05 wt. and preferably within the rangefrom 0.01 to 0.03 wt. by control of the substantially completecombustion of coke therefrom, together with substantially completecombustion of carbon monoxide gas in the presence of catalyst particles,with enhanced recovery of the evolved heat of combustion by heatingcatalyst particles and mass transfer of the heated catalyst particles tothe conversion process. The process employs an unusually high andsustained regeneration temperature which requires carefully balancedcontrols to maintain the temperature sufficiently high to affordsubstantially complete combustion of carbon monoxide while notpermitting the temperature to range so high that catalyst particlesbecome thermally deactivated or that the regeneration vessel andinternals become unsafe or inoperative. The temperature mayadvantageously range from about l200 to about 1500F., desirably fromabout l250 to about 1450F., although in some instances temperatures aslow as about 1 l50F. within lower regions of the regeneration vesselhave been satisfactory.

This invention is particularly useful in the fluid catalytic conversionof petroleum feedstocks and is advantageously employed where at least asubstantial portion of the conversion is effected in a dilute-phasetransfer line or riser reactor system. This invention makes possible anenhanced degree of energy conservation within a cyclic process for thecatalytic conversion of petroleum feedstocks which includes provisionfor separation of catalyst from conversion products, regeneration of theseparated catalyst and recycle of the regenerated catalyst to thereactor for the conversion of additional feedstock, wherein an increasedproportion of heat energy is utilized within the cyclic system byimproved continuous transfer from the exothermic to the endothermicprocessing zones. A particularly suitable petroleum conversion processfor the practice of this invention comprises the fluid catalyticcracking process for the conversion of petroleum gas oils and heavierpetroleum stocks to hydrocarbon components suitable for blending intofuels for automotive engines, jet power plants, domestic and industrialfurnaces, and the like.

The process of this invention contemplates the contacting of a stripped,deactivated petroleum conversion catalyst, such as a fluidizablehydrocarbon-cracking catalyst deactivated by the deposition thereon ofcarbonaceous deposits or coke and stripped with steam, with anoxygen-containing regeneration gas in a regeneration vessel which maysuitably be adapted to the countercurrent flow of catalyst andregeneration gas. Substantially complete regeneration of catalystparticles, accomplished by the combination of carbonaceous deposits orcoke, may occur in one relatively dense catalyst bed together withcombustion of substantially all carbon monoxide present to carbondioxide. More frequently, substantial regeneration of catalyst particlesoccurs in one or more relatively dense fluidized catalyst zonescontained within a first or primary regeneration zone situated in thebottom section of the regeneration vessel. Combustion is effected byproviding to the dense zone or zones at combustion temperature aquantity of regeneration gas, passing upwardly, sufficient to afford atleast an amount of oxygen equal to that required stoichiometrically forthe complete oxidation of carbon monoxide formed in the course ofoxidation of the coke. Partially spent regeneration gas leaving thelower section, comprising carbon monoxide, carbon dioxide and oxygen,contained suspended or entrained particles of at least partiallyregenerated catalyst. The partially spent regeneration gas passes fromthe dense-bed zone to a relatively dilute-phase, fluidized and dispersedsecond regeneration zone, wherein the combustion of carbon monoxide issubstantially completed at a temperature suitably maintained above about1250F., and desirably above about 1300F., by suitably controlling meansso that the temperature within the second regeneration zone does notexceed about 1500F. and advantageously does not greatly exceed about1450F. The regeneration temperature within the dense bed is maintainedat a temperature within the range from 1 150 to l400F., desirably about1250F., to initiate and sustain the further oxidation of carbon monoxideto carbon dioxide.

Somewhat lower temperatures may be employed where an added CO combustioncatalyst is present.

Catalyst particles from the dilute phase, now essentially completelyfreed of coke deposits, are largely separated from the hot regenerationgas stream by passage into a series of cyclones with the catalystparticles being returned to the dense-phase zone by means of cyclonedip-legs. Alternatively, the regenerated catalyst particles from thedilute phase may pass directly from the cyclone dip-legs to a suitablestandpipe or hopper means for return directly to the conversisonreactor. The flue gas stream, usually containing some oxygen butsubstantially free of carbon monoxide, is discharged to the atmosphereor passed through suitable heat-exchange means for recovery of thesensible heat of the gases.

Although temperature control within the secondary dilute-phaseregeneration zone may be effected in part by addition of steam or by awater spray, directed preferably into the region of the cyclones andother internal portions of the regeneration vessel structure, the dilutecatalyst phase is desirably loaded with as much catalyst as required forthe heat of combustion of CO to be absorbed by the catalyst particlesprior to their entry into the cyclones and return to the dense-bedcatalyst phase.

Suitably controlled and balanced loading of the dilute phase may, forexample, be effected by employing a suitable gas velocity through thedense-bed zone or catalyst advantageously may be circulated by asuitable cycling means from the dense phase into the dilute phase zone.The cycling of catalyst may, for example, suitably be effected by meansof an independently controlled eductor or catalyst-lift system toachieve an enhanced transfer of heat to the catalyst particles.

Regenerated catalyst particles, having an unusually low residual cokecontent, are finally recovered from the dense-phase zone and passed atsubstantially densebed temperature through a standpipe to the conversionreactor for contacting with fresh hydrocarbon feed or a mixture thereofwith recycled hydrocarbonfractions. When this novel technique isincorporated in the fluid catalyst cracking process, regeneratedcatalyst can be returned to the cracking reactor at-a much highertemperature as well as higher activity than in heretofore conventionaloperations.

Many fluid catalytic cracking units are operated on the heat balanceprinciple, depending upon combustion of coke for the evolution of heatrequired in the process. Such units have not been able to fully utilizethe potential benefits of the highly active zeolite or molecular sievecatalysts which can especially be achieved in riser reactors wherecontact times between catalyst and oil vapors may be extremely short.The type of op eration which affords high conversion coupled with highselectivity favors a low ratio of catalyst to oil in the riser whichleads to less coke being available for generation of combustion heat inthe regenerator. Accordingly an external heat soruce such as a feedpre-heat furnace, must be added or, alternatively, the unit must beoperated at a lower throughput of fresh feed. Such undesirable featuresare avoided by the process of this invention which permits efficientrecovery of additional heat for transfer by regenerated catalystparticles to the riser reactor. The heat of combustion of coke inconventional operations is about 12,000 BTU/lb. The process of thisinvention increases the available heat to about 17,000 BTU/lb. Thishigher heat of combustion raises the regenerator temperature, lowers thelevel of coke on regenerated catalyst and lowers the catalystcirculation rate while providing improved yields at a given conversionlevel.

The attached drawings, FIGS. 1 and 2, are illustrative, withoutlimitation, of embodiments of this invention. Regeneration of spentcatalyst from any suitable petroleum conversion process can be effectedin an improved manner by the novel process of this invention. Indeed,this improved process may be employed benefially in many existingpetroleum conversion process units, particularly fluid catalyticcracking units without limitation as to the spatial arrangement ofcracking, stripping end regeneration sections thereof.

FIG. 1 is illustrative of one embodiment of this invention employingbottom entry of stripped, spent catalyst to the regenerator. Spentcatalyst particles from a stripping zone enter from the bottom ofregeneration vessel 1, flowing upwardly through inlet lines 2 and 3 anddischarging into the dense catalyst bed through discharge heads 4 and 5.The dense-phase catalyst bed is maintained within the bottom section 6of the regenerator vessel and extends upwardly to the catalyst phaseinterface 7. Catalyst within the dense-phase bed is fluidized by theflow of combustion air through line 8, valve 9 and line 10 to air ring11. Substantially balanced air flow patterns through the regenerationzones may be achieved by the use of additional air rings, not shown, asrequired. Combustion of coke contained on the spent catalyst with air isinitiated within the densephase bed. Higher temperatures may be achievedby temporarily burning a stream of torch oil, for example a decantedoil, witin the bed. Torch oil may be added by passage through line 12,valve 13 and 14 which terminates in a nozzle located above the air ring11. Fluidizing air velocities continuously carry some of the catalystparticles upwardly into the dilute-phase zone which occupies the uppersection 15 of the regenerator vessel; i.e., the section above thecatalyst phase interface 7. Combustion of coke continues in thedilute-phase zone and the largely spent combustion gas together withentrained catalyst finally is withdrawn into cyclone separators and 21.Most of the catalyst particles are separated in the first-stage cyclonesand discharged downwardly through dip-legs 22 and 23 into thedense-phase zone. Gases and remaining catalyst particles are passedthrough interstage cyclone lines 24 and 25 to secondstage cycloneseparators 26 and 27 where substantially all of the remaining catalystis separated and passed downwardly through dip-legs 28 and 29 into thedensephase bed. Substantially spent combustion gas then passes throughlines 30 and 31 into plenum 32 and finally is discharged from theregenerator vessel through line 33. This may be followed by suitableheat exchange, not shown, with refinery stream or for production ofprocess steam. Regenerated catalyst from the dense bed is withdrawnthrough stand pipes 34 and 35, fitted with collector heads 36 and 37,for return to the catalytic conversion process.

Although the supply of combustion air normally provides an excess ofoxygen over the amount required to effect complete combustion of thecoke on the catalyst particles to steam and carbon dioxide, combustionof coke is not completed in the dense-bed phase. Additionally, thecombustion gases rising from the densebed zone contain a substantialquantity of carbon monoxide as well as carbon dioxide and oxygen. Theremaining coke on catalyst and carbon monoxide are substantiallycompletely burned in the dilute-phase zone with evolution of much heat.When carbon monoxide burns in the dilute phase a high temperature zonewill usually be present throughout much of the dilutephase zone andparticularly at approximately the location indicated by X and canreadily be viewed through a window, not shown, at that horizontal plane.Control of regeneration temperature within the dilute-phase zone iseffected in part through absorption of heat by the mass of cataylstparticles either carried upwardly by the rising combustion gas stream oreducted upwardly from the dense bed through educator tube 40 andcataylst distributor head 41 where a rain, or fountain, of catalystparticles disperses into the dilute-phase zone. Catalyst is educated bymeans of air, steam or other inert gas entering through line 42, valve43 and jet tube 44 which extends a short distance into the lower end ofeductor tube 40. Excessive temperature levels in the top section of theregenerator may be further controlled by distrubution of steam, forexample through lines 45 and 46, valve 47 and line 48 to steam pod 49.Temperatures in the vicinity of the plenum may also be controlled withsteam fed through line 50, valve 51 and line 52 to steam ring 53 whichsurrounds plenum 32. Additional cooling if desired may be provided byuse of a water spray, not shown, which may advantageously be directedwithin the region of interstage cyclene lines 24 and 25.

FIG. 2 is illustrative of an embodiment of this invention employing sideentry of stripped, spent catalyst to the regenerator and providing a netcountercurrent flow of catalyst and regeneration gas. Spent catalystenters regeneration vessel 101 flowing downwardly through inlet line 102located on the side of the regeneration vessel to provide entry into thedense-phase catalyst bed maintained within bottom section 106 a shortdistance below catalyst phase interface 107. Fluidization of catalystparticles within the dense-phase bed is effected by the flow ofcombustion air through line 108, valve 109 and line 110 to air ring 111.Additional air rings, not shown, may be employed as desired for furtherbalancing of air flow patterns through regeneration zones. As describedin FIG. 1, combustion of coke of the spent catalyst particles isinitiated within the dense-phase zone where higher temperatures asdesired may be achieved by temporary burning of a torch oil streamwithin the zone. Such torch oil may be added through line 112, valve 113and line 114 terminating in a nozzle. Fluidizing air velocity may becontrolled to continuously carry catalystparticles upwardly for purposesof heat absorption into the dilute-phase zone which occupies the uppersection 115 of the regenerator vessel; i.e., the section above thecatalyst phase interface 107. Combustion of coke as well as of carbonmonoxide continues in the dilute-phase zone and the largely spentcombustion gas together with the en trained portion of catalystparticles finally is withdrawn into cyclone separators and 121. Most ofthese catalyst particles are separated in the first-stage cyclones anddischarged downwardly through dip-legs 122 and 123 into the dense-phasezone. Genes and remaining catalyst subsequently pass through interstagecyclone lines 124 and 125 to second-stage cyclone separators 126 and 127where substantially all of the remaining catalyst is separated andpassed downwardly through dip-legs 128 and 129 into the dense-phase bed.Substantially spent combustion g as then passes through lines 130 and131 into plenum 132 and finally is discharged from the regeneratorvessel through line 133. Regenerated catalyst from the dense bed iswithdrawn through standpipes 134 and 135, fitted with collector heads136 and 137, for return to the catalytic conversion process. I

As described for FIG. 1, carbon monoxide burns in the dilute phaseproviding a high temperature zone throughout much of the dilutephasezone and particularly at approximetely the location indicated. by X.Control of regeneration temperature within the dilutephase zone iseffected largely through absorption of heat by the mass of catalystparticles carried upwardly by the rising combustion gas stream.Temperatures in the vicinity of the plenum, cyclone and connecting linesmay, as required, be reduced with steam fed through line 150, valve 151and line 152 to steam ring 153 which surrounds plenum 132. Water spraymeans, not shown, may similarly be employed.

Suitable petroleum fractions include light gas oils, heavy gas oils,wide-cut gas oils, vacuum gas oils, kerosenes, decanted oils, residualfractions, reduced crude oils and cycle oils derived from any of these,as well as suitable fractions derived from shale oil, tar sandsprocessing, synthetic oils, coal hydrogenation and the like. Suchfractions may be employed singly or in any desired combination.

Suitable catalysts include those containing silica and- /or alumina.Other refractory metal oxides such as magnesia or zirconia may beemployed limited only by their ability to be effectively regeneratedunder the selected conditions. With particular regard to catalyticcracking, preferred catalysts include combinations of silica andalumina, containing 10-50 wt. alumina and particularly their admixtureswith molecular sieves or crystalline aluminosilicates. Admixtures ofclayextended aluminas may also be employed. Such catalysts may beprepared by any suitable method such as impregnation, milling,cogelling, and the like, subject only to provision of the finishedcatalyst in a physical form capable of fluidization.

Suitable molecular sieves include both naturallyoccurring and syntheticaluminosilicate materials, such as faujasite, chabazite, X-type andY-type aluminosilicate materials, and ultrastable, large-porecrystalline aluminosilicate materials. The metal ions contained thereinare exchanged in large part for ammonium or hydrogen ions by knowntechniques. When admixed with, for examble, silica-alumina to provide apetroleum crackling catalyst, the molecular sieve content of the freshfinished catalyst particles is suitably within the range from 5 to wt.desirably 8-10 wt. An equilibrium molecular-sieve cracking catalyst maycontain as little as about 1 wt. crystalline material.

The stripping vessel is suitable maintained essentially at conversionreactor temperature in the range from 850 to 1050F. and desirably willbe maintained at about 950F. Preferred stripping gas is steam althoughnitrogen, other inert gas or flue gas may be employed, introduced at apressure, usually in the range from 10 to 35 p.s.i.g., suitable toeffect substantially complete removal of volatile components from thespent conversion catalyst. Stripped spent catalyst particles enter thedense-bed section of the regenerator'vessel through suitable lines andvalving fromthe stripping vessel.

Entry may be from the bottom or from the side, desirably near the top ofthe dense-bed fluidized zone. The dense-phase fluid-bed regenerationstage (or stages) is usually maintained at a pressure in the range from5 to 50 p.s.i.g. and a temperature in the range from 1150 to 1400F.,desirably about l250F. The regeneration gas may be air, oxygen,oxygen-enriched air or other oxygen-containing gas mixture suitable forcombustion of coke deposited on silica, alumina and/or aluminosilicatesurfaces. The regeneration gas enters the bottom dense-bed stage from ablower or compressor. A fluidizing velocity suitably in the range from0.2 to 4 feet/- second, desirably about 0.5 to about 3 feet/second, ismaintained in the dense-bed regeneration stage (or stages).

The regeneration gas fluidizing the dense-bed is suitably charged to theregenerator in an amount somewhat in excess of that required forcomplete combustion of coke (carbon and hydrogen) to carbon dioxide andsteam. The excess of oxygen may vary from about 0.1 to about 25% of thetheoretical oxygen requirement but advantageously need not be greaterthan about 10%. For example, when air is employed as the regenerationgas in a 10% excess of air provides only about 2 vol. oxygen in theeffluent spent gas stream.

Even though a substantial excess of oxygen be present in the dense-phasebed, combustion of both coke and carbon monoxide is conventionallyincomplete with the oxidized carbon being converted usually to a nearlyequimolar mixture of carbon monoxide and carbon dioxide. The materialrising from the dense-phase fluid bed should be hot enough to initiatethe complete combustion of carbon monoxide. Usually this requires atemperature level of at least about 1200F., desirably about 1275F. Thistemperature level may be initially attained by the burning of torch oilwithin the dense bed, with appropriate increase in the amount of oxygenintroduced into the regenerator, and thereafter carbon monoxidecombustion can be sustained with torch oil burning. Flame or sparkignition provides another suitable means for initiating the combustion.Although the regeneration gas rising into the dilute-phase zone usuallycontains from 2 to 10 vol. oxygen when employing air, sustained COcombustion may be aided by the injection of additional air or oxygen ata point just above the interface of the dense and dilute catalyst zones.The requisite temperature may be lowered by inclusion of a combustioncatalyst or promoter within the regeneration zone. For example, asuitable metallic bar or mesh network or screen may be inserted in thecombustion zone. Alternatively, fluidizable metal compounds,particularly powdered oxides of transition group metals, e.g., ferricoxide (Fe O manganese dioxide (MnO rare earth oxides and the like may beadded to the catalyst charge or confined on catalyst trays situated inthe regenerator vessel. For example, iron oxide powder fluidizable withthe conversion catalyst may be added to the catalyst in an amountup toat least about 0.5 wt. desirably about 0.2 wt. %,'with no observableharmful effects on the catalyst or the conversion process. Use of suchreagents may lower the temperature required to initiate and sustaincombustion by as much as about F.

Although further combustion of carbon monoxide occurs quite rapidly atthe maintained dense-bed temperature, much of this combustion actuallyoccurs in the upper dilute-phase zone as the gas stream rapidly sweepsupwardly. Less catalyst is present in the dilute phase and with lessheat-absorbing medium the temperature rises rapidly. Combustion ofcarbon monoxide in the dilute-phase zone can be observed visuallythrough an observation port and appears as an intensely orange flame orfireball. The temperature within this zone is maintained higher than inthe dense-bed zone and advantageously maintained within the range fromabout l200 to about 1500F., desirably from about l250 to about 1450F.,and preferably from about 1300 to about 1400F. Such combustiontemperatures have historically been avoided in the petroleum conversionart because of concern for mechanical efficiency and stability andcatalyst quality. Effective temperature control in the dilute-phase zonemay be achieved by maximizing the heat transfer to catalyst particleswithin the dilute-phase section of the regenerator. This requiressignificantly increasing the incidence of catalyst particles in thedilute phase. This may be accomplished by any suitable means including,for example, increasing the gas velocity so that more catalyst is sweptinto the dilute phase or by otherwise loading the dilute phase with hotcatalyst from the dense-phase zone. Such loading may advantageously beaccomplished by external circulation of catalyst from the dense bed tothe dilutephase zone or by eduction within the regenerator vesselthrough a catalyst fountain to increase the catalyst densityappropriately. Such eduction may be effected with a controlled jet ofsteam, air, inert gas or a suitable combination thereof. This catalystheat sink so provided surprisingly absorbs in excess of 80% of the heatof CO combustion in the dilute-phase zone so that most of the heatenergy is conserved within the cyclic system for efficient use in theendothermic hydrocarbon conversion, or cracking, zone. Accordinglyexternal cooling, as by water or steam, need only be applied in un'usual instances to critical equipment at a few points within the topsection of the regenerator vessel. For example, steam cooling may beapplied to the plenum area and a water or steam spray system is madeavailable for application to the cyclones, interstage lines and cyclonehangers.

Catalyst within the dilute phase is partly carried into a separationzone, usually comprising cyclone separators arranged in a plurality ofstages, from which catalyst is returned directly through dip-legs to thedensebed zone and spent regeneration and combustion gases are collectedin a plenum and finally discharged for suitable recovery of the heatenergy contained therein. Recovery processes for heat from flue gasinclude steam generation, spent catalyst stripping, indirect heatexchange with various refinery streams and particularly with feed to theparticular conversion process, and employment in various drying orevaporation arrangements.

Recovery of heat by absorption in catalyst particles and return of thecatalyst to the dense phase serves also to assure maintenance of asuitably high temperature within the dense-phase zone. The dense-phasetemperature under relatively typical equilibrium conditions may closelyapproach about 1300F. so that combustion of the final increments ofdifficulty removable coke becomes substantially complete. Accordingly,regenerated catalyst from the dense-phase zone, suitably containing fromabout 0.1 to about 010 wt. desirably 0.01 to 0.05 wt. and preferablyabout 0.01 to about 0.03 wt. carbon, or coke, can be withdrawn from theregenerator at a temperature within the range from about l200 to about1450F., desirably from about 1250 to about 1300F., and returned to theconversion reactor for mixing therein with fresh petroleum feedstock,optionally together with recycle or other hydrocarbon stock, therebyeliminating the need for additional preheating of the feedstock.

The improved performance of the regenerated catalyst of this inventionis dramatically illustrated by the charts presented in FIG. 3.Laboratory studies on a gas oil fraction were conducted with a typicalsilicaalumina cracking catalyst, containing about 25 wt. alumina,designated as catalyst B, and with a molecular sieve catalyst,containing both silica-alumina and crystalline aluminosilicatecomponents, designated as catalyst A. Catalyst response to the carbonlevel on the catalyst after regeneration was measured in terms of degreeof conversion of feed and effect on gasoline yield (C -430F.) atconstant conversion. Over the broad range of residual carbon contentsstudied, the silicaalumina catalyst (catalyst B) was quite insensitivewhile the sieve-containing catalyst (catalyst A) was consis tently moresensitive to these parameters and extremely sensitive thereto at lowcarbon levels on catalyst. The incentive for removing coke from catalystas completely as possible, and certainly to a level below about 0.05 wt.is clearly apparent.

A further benefit from this novel regeneration pro' cess relates to theunusually low carbon monoxide content in the effluent gas stream fromthe regenerator. Whereas, flue gas from conventional regeneration ofcracking catalysts usually contain about 6 to 10% carbon monoxide, asimilar amount of carbon dioxide and very little oxygen, the flue gasfrom regeneration in accordance with this invention generally containsless than 0.2% and often no more than about 5500 ppm. carbon monoxide.The oxygen content of the flue gas is not critical and may vary fromabout 0.1 to about 10%, advantageously being within the range from 1 to3%. From an ecological point of view the extremely low level of carbonmonoxide in the flue gas stream is highly desirable and meets existingstandards for ambient air quality. Indeed, whenever required theremaining carbon monoxide may suitably be burned in the exhaust from theregenerator flue gas stack. From a process point of view, heat recoveryby downstream combustion of carbon monoxide in a CO boiler or afterburner arrangement is avoided, with consequent substantial savings inprocess equipment and operational costs.

Optimum use of this invention is an integral part of a fluid crackingunit employing a fluidizable cracking catalyst, such as a silicaaluminacatalyst having a crystalline aluminosilicate or molecular sievecomponent, in a transport, or riser reactor with attendant provision forstripping of spent, coked catalyst followed by regeneration of the spentcatalyst according to the process of this invention. Preferably,cracking occurs exclusively in the riser reactor and a following dancecatalyst bed in not employed. In the typical case where riser crackingis employed for conversion of a gas oil, the throughput ratio (TPR), orvolume ratio of total feed to fresh feed, may vary from 1.0 to 2.0. Theconversion level may vary from 40 to 100% and advantageously ismaintained above about 60%, for example, between about 60% and about Byconversion is meant the percentage reduction of hydrocarbons boilingabove 430F. at atmospheric by formation of lighter materials or coke.The weight ratio of catalyst to oil in the riser reactor may vary withinthe range from 2 to 10 so that the fluidized dispersion will have adensity within the range from 1 to 5 pounds/cubic foot. Desirably thecatalyst-oil ratio is maintained at no greater than about 5 andpreferably within the range from about 3 to about 5. The fluidizingvelocity may range from about 20 to about 60 feet/second. The riserreactor should preferably be substantially vertical, having a ratio oflength to average diameter at least about 25. For production of atypical naphtha product the bottom section mixing temperature within theriser reactor is advantageously maintained at about 1000F. forsubstantially complete vaporization of the oil feed so that the topsection exit temperature will be about 950F. Under these conditions,including provision for a rapid separation of spent catalyst fromeffluent oil vapor, a very short period of contact between catalyst andoil will be established. Contact time within the riser reactor willgenerally be within the range from about 3 to about seconds andpreferably within the range from about 3 to about 7 seconds. Shortercontact times are preferred because most of the hydrocarbon crackingoccurs during the initial increment of contact time and undesirablesecondary reaction are avoided. This is especially important if higherproduct yield and selectivity, including lesser coke production, is tobe realized.

Short contact time between catalyst particles and oil vapors may beachieved by various means. For example, catalyst may be injected at oneor more points along the length of a lower, or bottom, section of theriser. Similarly, oil feed may be injected at multiple points along thelength of the lower section of the riser reactor and different injectionpoints may be employed for fresh and recycle feed streams. The lowersection of the riser reactor may, for this purpose, include up to about80% of the total riser length in order to provide extremely shorteffective contact times conducive to optimum conversion of petroleumfeeds. Where a following dense catalyst bed is employed, provision mayalso be made for injection of catalyst particles and/or oil feeddirectly into the dense bed zone.

Although the conversion conditions set forth above are directed to theproduction of gasoline as fuel for spark-ignition internal combustionengines, the processing scheme may be suitably varied to permit maximumproduction of heavier hydrocarbon products such as jet fuel, Diesel fueland heating oils.

EXAMPLES The following examples are illustrative of the process of thisinvention without limitation on the scope thereof.

EXAMPLE I Mid-continent gas oil (234 API) having a boiling range from650 to 1050F. was cracked in a fluidized transport-type reactor at anaverage cracking temperature of 960F. The throughput ratio (weight totalfeed/- weight fresh feed) was 1.34 and the total feed rate was 36,000bbl/day. The catalyst particles comprised silicaalumina together with 10wt. crystalline aluminosilicate or molecular sieve material andcirculated at a rate of 19.6 tons/minute. The weight ratio of catalystto oil in the cracking zone was 3.7.

Effluent from the riser reactor was passed to a separation zone and fedinto a cyclone separator. Hydrocarbon products were removed and spentcatalyst was passed downwardly through the cyclone dip-leg into astripping zone maintained at 950F. The settled catalsyt was strippedwith steam to remove remaining volatile material prior to regeneration.

Stripped spent catalyst, containing 0.9 wt. coke on catalyst, was fedinto the bottom section of a regenerator vessel where it was fluidizedwith air in a densephase catalyst bed maintained at l250l275F. (aver agetemperature was 1260F.) by combustion of coke and occasional combustionof torch oil as required. The air rate was set to provide approximately14.0 lbs. air per lb. coke on spent catalyst. Some catalyst wasentrained in the rising air stream and carried into the dilute-phasecatalyst zone in the upper portion of the regenerator vessel about theinterface with the dense bed. Additional catalyst was swept upwardthrough three eductor tubes, each fitted with a dispensing head, with ajet stream of steam and dispersed to provide a descending fountain ofcatalyst. Combustion of carbon monoxide within the dilute-phase zoneproduced a fireball visible through a viewing port in the side wall ofthe regenerator. The temperature in the area near the fireball was aboutl450F. Gases and entrained catalsyt were passed from the dilute-phasezone into a series of cyclone separators with catalyst being returneddirectly to the dense-phase zone. The temperature at the cyclone inletwas held at approximately 1400F. with catalyst and water spray asrequired, the water spray being directed below the inlet of the cyclonesystem. The gas stream leaving the cyclone system was passed first to aplenum area located at the top of the top of the regenerator vessel andthen was discharged at 1250F. Catalyst was withdrawn from thedense-phase bed as required through a standpipe at 1250F. for return tothe transport reactor.

Analysis of the regenerated catalyst indicated the residual coke contentto be only 0.03 wt. The catalyst particles were white to light gray incolor. Analysis of the effluent gas indicated the carbon monoxidecontent to be 0.0 vol. and the oxygen content to be 1.9 vol. Thecracking conversion was 67.7 vol. on feed. From heat balancecalculations coke was burned at the rate of 20,700 lbs./hr., liberating17,800 BTU/lb. coke. Of the total heat evolved, over was absorbed in theregenerated catalyst and thus kept within the cyclic fluid crackingsystem.

EXAMPLE II Three test periods on a commercial fluid catalytic crackingpetroleum conversion unit are compared with prior operations on the sameunit at similar conversion levels and feed rates in Table I. Thecatalyst employed was of the molecular sieve type and the hydrocarbonfeed was a typical Mid-continent type gas oil. The comparisons clearlyshow an improvement in gasoline naptha (C -430F.) yield. With the lowercoke level on both spent and regenerated catalyst and correspondinghigher activity, the catalyst circulation rate (which controls thecatalyst-oil ratio) is lowered to hold a selected conversion level. Thecarbon monoxide content of the effluent gas is significantly diminishedand indeed can be reduced to nearly 0.0 vol.

EXAMPLE 111 Two test periods on the same commercial unit are compared inTable II with calculated data based on computer-programmed simulation(i.e., conventional) runs at identical feed rate, conversion level andcracking reactor average temperature. The weight ratio of catalyst tooil is greatly reduced, reflecting the lower circulation rate adequateto achieve the desired con- 2 version, when catalyst is regeneratedaccording to the process of this invention. The yield of C;,-430F.naphtha is significantly increased with little change apparent inlighter products. There is a significant decrease in the coke yield withthis increment being converted to valuable cracked products. Thegasoline yield is not only increased but the octane number is alsohigher,

thus providing more barrel-octanes for blending pur poses from a givenamount of feed.

EXAMPLE IV Test conditions similar to those of Example I (but withoutthe eductor tube in use) were employed to determine the minimum level ofcarbon monoxide content reasonably to be achieved in the regeneratorstack. The amount of excess air was varied while maintaining the densefluidized bed temperature within the regenerator at about 12901300F. andsampling effluent gases from the stack. Results set forth in Table 111clearly show that carbon monoxide levels as low as 8 ppm. can readily beachieved by the process of this invention. Modest extrapolation of thesedata suggests that it is not unreasonable to anticipate operation withno detectable amount of carbon monoxide in the stack gas.

TABLE 1 COMPARATIVE CA'I ALYST REGENERATION TESTS Test Period 1 2 3 A BA 15 A B Feed. MB/D 29.9 29.4 41.0 40.6 39.7 38.0 Conversion, vol. '7:68.0 71.5 61.4 59.4 66.3 67.4 Reactor Av. Temperature, I-'. 942 960 946940 960 900 Pressure, p.s.i.g. 17.1 20.0 19.2 21.3 18.6 20.5 Catalystcirculation, tons/min. 20.6 28.1 21.7 34.5 21.9 29.4 Catalyst-oil wt.ratio 5.2 6.0 4.1 6.5 4.2 5.4 Regcnerator Dense Bed Temperature, F. 12181204 1236 1 173 1255 1204 Cvclone Inlet Temperature, F. 1380 1210 13761140 1388 1185 C6ke burn. M 1b./hr. 18.3 25.5 20.5 28.7 21.3 28.1 Carbonon spent cat. wt. "/1 0.85 1.18 0.77 1.00 0.80 0 97 Carbon on rcgen.cat, wt. 7( 0.05 0.37 0.04 0.35 0.03 0.22 Wt. ratio. air/coke 14.7 11.214.0 11.2 14.6 11.4 Effluent gas, vol. "/1

CO 16.0 10.6 16.4 10.0 16.0 10.6 Co 0.0 9.4 0.5 9.6 0. 9.0 O" 1.7 0.41.0 0.4 2.1 0.7 Products Dry gas 1- C;,, Wt. Z 7.8 9.7 6.7 6.9 8.6 8.2Iso-butane, vol. '7! 4.6 6.2 4.0 4.5 4.0 5.1 N-hutane vol. k 1.4 1.6 1.32.2 1.3 1.3 Butenes vol. "/1 7.0 7.4 6.6 5.8 7.2 8.0 C-,430F. vol. '/I56.8 52.2 51.1 47.0 54.3 51.9 Cbkc, wt. /1 4.7 6.6 3.9 4.9 4.1 5.7

A Test Period B Prior Operation TABLE I1 COMPARISON OF ACTUAL ANDSIMULATION DATA Test Period 1 2 Simulated Actual Simulated Actual Feed,B/D 41.378 41,378 35,904 35.904 Conversion. vol. 61.8 61.8 67.7 67 7Reactor Av. Temperature, F. 944 944 960 960 Catalyst Circulation,tons/min. 5,9 19}; 37 5 l9; Cata1ystoi1 ratio 5.3 3.5 6.1 3.7Regenerator Dense Bed Temperature F. 1143 1245 1 43 25 Cyclone InletTemperature, "F. 1383 1371 Coke burn, M 1b./hr. 30.03 20.02 29.03 20.72Carbon on spent cat. wt. "/1 1.06 0.86 0.96 0.91 Carbon on g nat. t.0.34 0.03 0.34 0.03 Products C and lighter. vol. 71 11.84 11.87 14.6715.99 Iso-butane 5.24 3.43 5.85 4.20 N-hutane 1.49 0.98 1.74 0.94Butenes 6.33 5.98 7.57 7.13 Pentanes 4.19 3.27 4.83 3.14 Pentenes 3.653.48 4.00 4.16 46.96 51.05 49.88 52.70 Coke, Wt. '71 5.54 3.70 6.15 4.39Gasoline Octane 89.75 90.4 89.7 90.3 No.

Table III Effect of Excess Oxygen on Carbon Monoxide Content of StackGas Regencrator Stack Gas Analysis "Oxygen analyses obtained with Hays.Acratmn. Serial M2990. -57: scale.

"Carbon monoxide analyses obtained with Union Carbide. Modcl 3020.Carbon Monoxide Analyser.

"Carbon dioxide analyses obtained by Orsat method.

It is claimed:

1. In a process for catalytically cracking petroleum feedstock whereinfluidizable cracking catalyst which has been deactivated with cokedeposits is withdrawn from the cracking reaction zone, stripped ofvolatile material, passed to a regeneration zone, and recycled afterregeneration to the reaction zone, the method comprising:

a. contacting deactivated, coked catalyst particles withoxygen-containing regeneration gas to provide an excess of oxygen in aregeneration zone and burning substantially all of the coke from thecata lyst particles at regeneration temperatures;

b. initiating and sustaining combustion of carbon monoxide produced bysaid burning through contact with oxygen-containing gas in theregeneration zone at a temperature sufficient to combust substantiallyall of the carbon monoxide in the regeneration zone but not so high thatsaid cracking catalyst is thermally deactivated;

. providing a sufficient amount of catalyst in the regeneration zone toabsorb a major portion of the heat of combustion liberated by saidcombustion of carbon monoxide and to maintain said carbon monoxidecombustion temperature; d. conducting said substantially completecombustion of carbon monoxide in the regeneration gases undergoingcombustion, with the velocity of gases in the regeneration zone beingsuch to provide contact of said regeneration gases with fluidizedcracking catalyst particles in an amount sufficient to absorb a majorportion of the heat of combustion liberated by said combustion of carbonmonoxide and to maintain said carbon monoxide combustion temperature;absorbing said major portion of the heat of combustion of carbonmonoxide in said fluidized cracking catalyst particles in directheat-exchange contact with regeneration gases undergoing combustion insaid regeneration zone and thereby maintaining said temperature forcombusting substantially all of the carbon monoxide in the regenerationzone; f. withdrawing from the regeneration zone effluent gas having alow content of carbon monoxide; and

g. withdrawing from the regeneration zone regenerated catalyst particleshaving a low content of residual coke for passage to said reaction zone.

2. The process of claim 1 wherein said cracking catalyst comprisessilica, alumina and crystalline aluminosilicate.

3. The process of claim 1 wherein said combustion of carbon monoxide isat a temperature of about 1250F. to about 1450F.

4. The process of claim 3 wherein said withdrawn regeneration zoneeffluent gas contains no more than about 0.2 volume carbon monoxide andsaid withdrawn regenerated catalyst particles contain no more than about0.05 weight coke.

5. The process of claim 4 wherein regeneration gases undergoingcombustion are in contact with an amount of fluidized cracking catalystparticles sufflcient to absorb greater than about of the heat ofcombustion liberated by said combustion of carbon monoxide.

6. The process of claim 5 wherein said cracking catalyst comprisessilica, alumina and crystalline aluminosilicate.

7. The process of claim 6 wherein the cracking reaction zone is in acracking reaction vessel of the transport type.

8. In a process for catalytically cracking petroleum feedstock whereinfluidizable cracking catalyst which has been deactivated with cokedeposits is withdrawn from the cracking reaction zone, stripped ofvolatile material, passed to a regeneration zone, and recycled afterregeneration to the reaction zone, the method comprising:

a. contacting deactivated, coked catalyst particles withoxygen-containing regeneration gas to provide an excess of oxygen in alower dense-phase catalyst section of the regeneration zone and burningtherein substantially all of the coke from the catalyst particles atregeneration temperatures;

b. initiating and sustaining combustion of carbon monoxide produced bysaid burning through contact with oxygen-containing gas in an upperdilute-phase section of the regeneration zone to combust substantiallyall of the carbon monoxide in the regeneration zone;

c. circulating fluidized regenerated cracking catalyst particlesupwardly from said lower dense-phase section into said upperdilute-phase section in an amount sufficient to absorb a major portionof the heat of combustion liberated by said combustion of carbonmonoxide;

d. absorbing said major portion of the heat of conr bustion of carbonmonoxide in said circulated fluidized regenerated cracking catalystparticles in direct heat-exchange contact in said upper dilutephasesection with said regeneration gas;

e. withdrawing from the regeneration zone effluent gas having a lowcontent of carbon monoxide; and

. withdrawing from the regeneration zone regenerated catalyst particleshaving a low content of residual coke for passage to said reaction zone.

9. A cyclic, continuous process for fluid catalytic cracking ofpetroleum hydrocarbons and catalyst regeneration, wherein active,fluidizable cracking conversion catalyst particles become spent whilecracking a petroleum hydrocarbon feedstock within a cracking reactionzone, spent catalyst particles containing coke are continuouslywithdrawn from the reaction zone and stripped in an inert gas stream,stripped spent catalyst particles are thereafter reactivated by burningcoke therefrom in a fluidized regeneration zone having a lowerdense-phase section and an upper dilute-phase section, maintained at aregeneration temperature sufficiently high to effect substantiallycomplete burning of coke, and hot regenerated cracking catalystparticles are recycled to said cracking reaction zone for use in saidfluid catalytic cracking, comprising the steps of:

a. introducing spent cracking catalyst particles, after stripping ofresidual volatile petroleum material, into a lower dense-phase sectionof a fluidized regeneration zone contained within a regeneration vesseland maintained at regeneration temperature;

b. introducing into the lower section of said regeneration zone anoxygen-containing regeneration gas stream in an amount in excess of thatrequired for complete combustion of the coke contained in the spentcatalyst particles and at an upward velocity sufficiently high to effectfluidization of said cracking catalyst particles;

c. burning coke from the spent cracking catalyst particles in contactwith said oxygen-containing regeneration gas stream in said lowersection of said regeneration zone at said regeneration temperature whilemaintaining said catalyst particles in a densephase fluidized state bythe upward flow of said oxygen-containing gas stream, to provide amixture comprising fluidized regenerated cracking catalyst particles,together with oxygen, carbon monoxide and carbon dioxide;

(1. substantially completing the combustion of carbon monoxide in saidregeneration gas stream to carbon dioxide in an upper dilute-phasesection of said regeneration zone at a temperature sufficiently high tosupport combustion of carbon monoxide;

e. circulating fluidized regenerated cracking catalyst particlesupwardly from said lower section into said upper section in an amountsufficient to absorb a major portion of the heat of combustion liberatedby said combustion of carbon monoxide;

f. absorbing said major portion of the heat of combustion of carbonmonoxide in said circulated fluidized regenerated cracking catalystparticles in direct heat-exchange contact in said upper section withsaid regeneration gas stream;

g. separating a spent regeneration gas stream, containing carbondioxide, excess oxygen and any unconverted carbon monoxide, fromentrained catalyst particles and discharging the spent regeneration gasstream from the regeneration vessel;

h. withdrawing regenerated cracking catalyst particles, substantiallyfree of coke and conserving the absorbed heat of combustion of saidcarbon monoxide, from said regeneration zone and introducing saidwithdrawn regenerated cracking catalyst particles into the crackingreaction zone; and

i. cracking a petroleum hydrocarbon feedstock with said regeneratedcracking catalyst particles in said cracking reaction zone underfluidizing conditions.

10. The process of claim 9 wherein the combustion of carbon monoxide issubstantially completed by controlling the temperature in the uppersection of the regeneration zone at a level higher than that maintainedin the lower section of the regeneration zone, while sustaining thecombustion of carbon monoxide with oxygen, at least in part by adjustingthe rate of curculation of regenerated cracking catalyst particles fromthe lower section of the regeneration zone.

11. The process of claim 9 wherein the oxygencontaining regeneration gasstream comprises air or oxygen-enriched air, flowing upwardly to providefluidization of the lower dense-phase section of the regeneration zone,the regeneration temperature within the lower section of theregeneration zone is maintained within the range from about ll50 toabout l400F., and the temperature within the upper section of theregeneration zone is maintained within the range from about l2()0 toabout l500F.

12. The process of claim 9 wherein the cracking catalyst particlescomprise silica and alumina together with crystalline aluminosilicate.

13. The process of claim 9 wherein the cracking reaction zone is afluidized catalytic cracking reaction zone, supplied with petroleumcracking catalyst consisting essentially of 35-89 wt. silica, 10-50 wt.alumina and l-l5 wt. crystalline aluminosilicate.

14. The process of claim 9 wherein the regenerated cracking catalystparticles contain no more than about 0.05 wt. coke and the spentregeneration gas stream contains no more than about 0.2 vol. carbonmonoxide.

15. The process of claim 9 wherein additional regenerated crackingcatalyst particles are circulated upwardly from the lower dense-phasesection of the regeneration zone into the upper section of theregeneration zone and dispersed within said upper section, in an amountsufficient to absorb substantially all of the evolved heat of combustionand in response to the temperature of the dilute-phase zone.

16. The process of claim 9 wherein at least about of the evolved heat ofcombustion of carbon monoxide is absorbed in the regenerated crackingcatalyst particles and transferred therein to the cracking reactionzone.

17. The process of claim 9 wherein the burning of carbon monoxide withinthe upper section of the regeneration zone initiated by burningsufficient torch oil within the dense-phase zone, while additionallyintroducing to said zone sufficient oxygen-containing gas to affordcomplete combustion of the torch oil, to provide a partially spentregeneration gas passing upwardly into said upper section at atemperature sufficiently high to sustain combustion of carbon monoxide,and thereafter ceasing the combustion of torch oil.

18. The process of claim 9 wherein the burning of carbon monoxide withinthe upper section of the regeneration zone is initiated by momentaryactuation of a spark-ignition means situated within and near the bottomof said upper section, and thereafter ceasing the spark ignition.

19. The process of claim 9 wherein the withdrawn regenerated crackingcatalyst particles are introduced into the cracking reaction zone at atemperature of at least about l,200F.

20. The process of claim 9 wherein the regenerated cracking catalystparticles are returned to the cracking reaction zone at substantiallythe temperature maintained in the lower dense-phase section of theregeneration zone.

21. The process of claim 9 wherein the cracking reac tion zone iscontained within a cracking reaction vessel of the transport type.

22. The process of claim 9 wherein the cracking of petroleum hydrocarbonfeedstock with regenerated cracking catalyst particles is effected insaid cracking reaction zone under fluidizing conditions providing acracking reaction time within the range from about 3 to about 10seconds.

23. A cyclic, continuous process for fluid catalytic cracking ofpetroleum hydrocarbons and catalyst regeneration, wherein coke is burnedfrom spent cracking catalyst particles in contact with an excess of anoxygencontaining regeneration gas stream in a fluidized dense-phaselower section of a regeneration zone and carbon monoxide from saidburning of coke is further burned to carbon dioxide in a dilute-phaseupper section of said regeneration zone in contact with sufficientcatalyst particles to absorb most of the heat of combustion of saidcarbon monoxide, comprising the step of circulating additional catalystparticles into the upper section of the regeneration zone through aneductor tube situated within the regenerator vessel, said eductor tubeextending substantially vertically from near the bottom of thedense-phase lower section to near the top of the dilute-phase uppersection of the regeneration zone and terminating in a distributing head,the eduction of catalyst being effected with ajet stream of a gasdirected upwardly into a bottom section of the eductor tube, whereby theadditional catalyst particles are lifted and dispersed substantiallyuniformly into a top portion of the upper section of the regenerationzone.

24. The process of claim 9 wherein spent catalyst particles and theoxygen-containing gas are introduced separately into a bottom section ofthe lower densephase section of the regeneration zone and regeneratedcatalyst particles are withdrawn from a top section of the lowerdense-phase section of the regeneration zone.

25. The process of claim 9 wherein spent catalyst particles are firstcontacted with an excess of an oxygen-containing regeneration gas in thelower densephase section of the regeneration zone maintained at atemperature within the range from about l,l50 to about 1,400F., andcarbon monoxide is thereafter substantially completely burned to carbondioxide within the upper dilute-phase section of the regeneration zone,at a temperature maintained within the range from about l,200 to aboutl,450F.

26. The process of claim 25 wherein regenerated catalyst particles arewithdrawn from the regeneration zone at a point near the top of thelower dense-phase section of the regeneration zone and at a temperatureof about 1,250F.

27. A cyclic, continuous process for fluid catalytic cracking ofpetroleum feedstock and catalyst regeneration, comprising the steps of:

a. continuously feeding petroleum feedstock and regenerated fluidizablecracking catalyst particles, said catalyst particles being at atemperature of at least about 1,200F., to a bottom section of a fluidcatalytic cracking reaction vessel in weight proportions selected toprovide a catalyst-oil ration within the range from about 2 to about 10;

b. mixing the fluidizable cracking catalyst particles with the petroleumfeedstock in said bottom section of the cracking reaction vessel,whereby the petroleum feedstock is substantially completely vaporized ata mixing temperature of about 1000F. to provide a fluidized mixture ofcatalyst particles and petroleum vapors;

c. passing the fluidized mixture of catalyst particles and petroleumvapors upwardly through the cracking reaction vessel at a fluidizingvelocity within the range from about 20 to about 60 feet per second,whereby the cracking reaction is effected and the cracking reaction timeis controlled within the range from about 3 to about 10 seconds;

d. continuously withdrawing a fluidized mixture of spent catalystparticles having carbonaceous material deposited thereon and petroleumvapors, including cracked petroleum vapor products, from a top sectionof the cracking reaction vessel at a temperature of about 950F., rapidlyseparating said spent cracking catalyst particles from said petroleumvapors, including cracked petroleum vapor products, and stripping saidseparated spent catalyst particles in an inert gas atmosphere at astripping temperature of about 950F.;

e. continuously feeding stripped spent cracking catalyst particles intoa lower section of a fluidized catalyst regeneration zone, containedwithin a catalyst regeneration vessel, together with an oxygencontainingregeneration gas in excess over the amount required for the completecombustion of the carbonaceous material deposited upon the spentcracking catalyst particles, said gas flowing at a fluidizing velocityupwardly through the regeneration zone, said fluidizing velocity beingwithin the range from about 0.5 to about 3 feet/second; burning a majorportion of the carbonaceous material from the spent cracking catalystparticles within the lower section of the fluidized catalystregeneration zone at a temperature maintained within the range fromabout 1 to about l400F., to provide a partially spent regeneration gascontaining carbon monoxide;

g. burning substantially all of the remaining carbonaceous material fromthe catalyst particles in the presence of the partially spentregeneration gas within an upper section of the fluidized catalystregeneration zone at a temperature maintained within the range fromabout l,200 to about h. simultaneously burning substantially all of thecarbon monoxide contained in the partially spent regeneration gas withinthe upper section ofthe fluidized catalyst regeneration zone at atemperature within the range from about l,200 to about l,450F.;

. circulating fluidized regenerated cracking catalyst particles upwardlyfrom said lower section into said upper section in an amount sufficientto absorb at least about 80% of the heat of combustion liberated by saidburning of carbon monoxide;

j. absorbing said major portion of the heat of combustion of carbonmonoxide in said circulated fluidized regenerated cracking catalystparticles in direct heat-exchange contact in said upper section withsaid regeneration gas stream;

k. discharging substantially spent regeneration gas, containing no morethan about 2000 ppm carbon monoxide together with from about 1.0 toabout lytic cracking reaction vessel is of the transport type.

29. The process of claim 27 wherein the cracking reaction time iscontrolled within the range from about 3 to about 7 seconds.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa e 1 OfPATENT'NO. 3,909,392 g 5 DATED September 30, 1975 Carl J Horecky Jr.Robert J. Fahrig; Robert J. Shields Jr. INVENTOMS) and Claude O.MdKinney It IS certrtred that error appears rn the above-rdentifiedpatent and that sard Letters Patent are hereby corrected as Shown belowColumn Line 1 57 "occur typical" should be occur under typical 2 12"After burning" should be Afterburning 2 60-61 "zeclites" should bezeolites 3 57 "densephase" should be dense-phase 4 6 "flud" should beflue 4 l0 "wihthin" should be within 4 2O "advantageous" should beadvantageously 4 26 "0.5" should be 0.05

5 31 The word "coke" should appear within quotation marks; 5 36"combination" should be combustion 5 6O "suitably" should be suitable 6ll "conversison" should be conversion 6 51-52 The words 'molecularsieve" should appear within quotation marks 6 59 "soruce" should besource 7 l2 "benefially" should be beneficially 7 15 "end" should be and7 34 "witin" should be within 7 35 "and 14" should be and line 14 8 l2"cataylst" should be catalyst 8 14-15 "cataylst" should be catalyst 8 l4"educator should be eductor 8 l7 "educated" should be educted 8 22"distrubution" should be distribution 8 29 "cyclene" should be cyclone 844-45 "through regeneration zones" should be through the regenerationzones Continued.

owner) sures PATENT OFFICE @ETEFEQATE 0F CORRECTION G PATENT NO-3,909,392

ATED September 30, 1975 C l J. H reck Jr. Robert J. Fahrig; Robert J.Shields Jr. mvENToms) aid Claud O. IcKinney t! rs certrtred that errorappears In the ab0ve|denti tred patent and that said Letters Patent arehereby corrected as shown below Page 2 Qf 5 Column Line 8 46 "of thespent catalyst" should be on the spent catalyst 8 51 "Fluidizing" shouldbegin a new paragraph; 8 63 "Genes" should be Gases 8 64 After"catalyst" add particles 9 ll "dilutephase" should be dilute-phase Q 9l2 "approximetely" should be approximately 9 36 "alumina and" should 'bealumina, and 9 37 The words "molecular sieves" should appear Withinquotation marks; 9 44 The words "molecular sieves" should appear withinquotation marks; 9 51 "examble" should be example 9 52 The words"molecular sieve" should appear within quotation marks; 9 55 The words"molecular sieve" should appear within quotation marks; 9 57 "suitable"should be suitably 1O 24 The word "in" should be deleted; Q 10 39 "with"should be without 10 59 Insert after "0.5 wt.%".

11 62 "difficulty" should be difficultly ll 65 "001" should be 0.01

. 12 13-14 The words "molecular sieve" should appear within quotationmarks;

12 40 After "3%" add and desirably no more than about 2%.

12 54 The Words "molecular sieve" should appear within quotation marks;12 59 "dance" should be dense 12 6O in not" should be is not QContinued.

INl'ifil) STATES PATENT OFFICE 1 r w 1 fi (1BR FIFHJATE ()l CORRELTIONPATENT NO. 3,909,392

DATED September 30, 1975 INVENTOWS, Carl J. Horecky, Jr.; Robert J.Fahrig; Robert J. Shields. Jr.;

and Claude O. McKinney it Is cemfaed thal error appears 1n theabove-ldentlfied patent and that said Letters Patent are herebycorrected as she-m beiow Page 3 of 5 Column Line 13 1 After"atmospheric" add pressure 13 26 "reaction" should be reactions 13 65The words "molecular sieve" should appear within quotation marks e 14 27"caxalsyt" should be catalyst l5 9 Before "circulation" add catalyst 2023 "curculation" should be circulation 2O 64 After "zone" add is 22 16"ration" should be ratio 24 7 Before l,2OOF." add "about".

lgncd and Scaled this thirtieth a 0 March 1976 [SEAL] D y f Arrest.

RUTHV C. MAnsoN C. MARSHALL DANN Q "nesmlg 011m (ummissimu'r uj'PaIenIsand Trademarks

1. IN A PROCESS FOR CATALYTICALLY CRACKING PETROLEIUM FEEDSTOCK WHEREINFLUIDIZABLE CRACKING WHICH HAS BEEN DEACTIVATED WITH COKE DEPOSITS INWITHDRAWN FROM THE CRACKING REACTION ZONE STRIPPED OF VOLATILE MATERIAL,PASSED TO A REGENERATION ZONE, AND RECYCLED AFTER REGENERATION TO THEREACTION ZONE, THE METHOD COMPRISING: . CONTACTING DEACTIVATED, COKEDCATALYST PARTICLES WITH OXYGEN-CONTAINING REGENERATION GAS TO PROVIDE ANEXCESS OF OXYGEN IN A REGENERATION ZONE AND BURNING SUBSTANTIALLY ALL OFTHE COKE FROM THE CATALYST PARTICLES AT REGENERATION TEMPERATURES, B.INITIATING SUSTAINING COMBUSTION OF CARBON MOMOXIDE PRODUCE BY SAIDBURNING THROUGH CONTACT WITH OXYGENCONTAINING GAS IN THE REGENRATIONZONE AT A TEMPERATURE SUFFICIENT TO COMBUST SUBSTANTIALLY ALL OF THECARBON MONOXIDE IN THE REGENERATION ZONE BUT NOT SO HIGH THAT SAIDCRACKING CATALYST IS THERMALLY DEACTIVATED, C. PROVIDING A SUFFICIENTAMOUNT OF CATALYST IN THE REGENERATION ZONE TO ABSORBED A MAJOR PORTIONOF THE HEAT OF COMBUSTION IBERATED BY SAID COMBUSTION OF CARBON MONOXIDEAND TO MAINTAIN SAID CARBON MONOXIDE COMBUSTION TEMPEATURE, D.CONDUCTING SAID SUBSTANTIALLY COMPLETE COMBUSTION OF CARBON MONOXIDE INTHE REGENERATION GASES UNDERGOING COMBUSTION, WITH THE VELOCITY OF GASESIN HE REGENERATION ZONE BEING SUCH TO PROVIDE CONTACT OF SAIDREGENERATION GASES WITH FLUIDIZED CRACKING CATALYST PARTICLES IN ANAMOUNT SUFFICIENT TO ABSORB A MAJOR PORTION OF THE HEAT OF COMBUSTIONLIBERATED BY SAID COMBUSTION OF CARBON MONOXIDE, AND TO MAINTAIN SAIDCARBON MONOXIDE COMBUSTION TEMPERATURE, E. ABSORBING SAID MAJOR PORTIONOF THE HEAT OF COMBUSTION OF CARBON MONOXIDE IN SAID FLUIDIZED CRACKINGCATALYST PARTICLES IN DIRECT HEAT-EXCHANGING CONTACT WITH REGENERATIONGASES UNDERGOING COMBUSTION IN SAID REGENRATION ZONE AND THEREBYMAINTAINING SAID TEMPERATURE FOR COMBUSTING SUBSTANTIALLY ALL OF THECARBON MONOXIDE IN THE REGENERATION ZONE, F. WITHDRAWING FROM THEREGENERATION ZONE EFFLUENT GAS HAVING A LOW CONTENT OF CARBON MONOXIDE,AND G. WITHDRAWING FROM HE REGENERATION ZONE REGENERATED CATALYSTPARTICLES HAVING A LOW CONTENT OF RESIDUAL COKE FOR PASSAGE TO SAIDREACTION ZONE.
 2. The process of claim 1 wherein said cracking catalystcomprises silica, alumina and crystalline aluminosilicate.
 3. Theprocess of claim 1 wherein said combustion of carbon monoxide is at atemperature of about 1250*F. to about 1450*F.
 4. The process of claim 3wherein said withdrawn regeneration zone effluent gas contains no morethan about 0.2 volume % carbon monoxide and said withdrawn regeneratedcatalyst particles contain no more than about 0.05 weight % coke.
 5. Theprocess of claim 4 wherein regeneration gases undergoing combustion arein contact with an amount of fluidized cracking catalyst particlessufficient to absorb greater than about 80% of the heat of combustionliberated by said combustion of carbon monoxide.
 6. The process of claim5 wherein said cracking catalyst comprises silica, alumina andcrystalline aluminosilicate.
 7. The process of claim 6 wherein thecracking reaction zone is in a cracking reaction vessel of the transporttype.
 8. IN A PROCESS FOR CATALYTICALLY CRACKING PETROLUEM FEEDSTOCKWHEREIN FLUIDIZABLE CRACKING CAALYST WHICH HAS BEEN DEACTIVATED WITHCOKE DEPOSITS IS WITHDRAWN FROM THE CRACKING REACTION ZONE, STRIPPED OFVOLATILE MATERIAL, PASSED TO A REGENREATION ZONE, AND RECYCLED AFTERREGENERATION TO THE REACTION ZONE , METHOD COMPRISING: A. CONTACTINGDEACTIVATED, COKED CATALYST PARTICLED WITH OXYGEN-CONTAININGREGENERATION GAS TO PROVIDE AN EXCESS OF OXYGEN IN A LOWER DENSE-PHASECATALYST SECTION OF THE REGENERATION ZONE AND BURNING THEREINSUBSTANTIALLY ALL OF THE COKE FROM THE CATALYS PARTICLES AT REGENERATIONTEMPERATURES, B. INITIATING AND SUSTAINING COMBUSTION OF CARBON MONOXIDEPRODUCED BY SAI BURING THROUGH CONTACT WITH OXYGENCONTAINING GAS IN ANUPPER DILUT-PHASE SECTION OF THE REGENERATION ZONE TO COMBUSTSUBSTANTIALLY ALL OF THE CARBON MONOXIDE REGENERATION ZONE, C.CIRCULATING FLUIDIZED REGENERATED CRACKING CATALYST PARTICLES UPWARDLYFROM SAID LOWER DENSE-PHASE SECTION INTO SAID UPPER DILUTE-PHASE SECTIONIN AN AMOUNT SUFFICIENT INTO ABSORB A MAJOR PAORTION OF THE HEAT OFCOMBUSTION LIBERATE BY SAID COMBUSTION OF CARBON MONOXIDE, D. ABSORBINGSAID MAJOR PORTION OF THE HEAT OF COMBUSTION OF CARBON MONOXIDE IN SAIDCIRCULATED FLUIDIZED REGENERATED CRACKING CATALYST PARTICLES IN DIRECTHEAT-EXCHANGING CONTACT IN SAID UPPER DILUTE-PHASE SECTION WITH SAIDREGENERATION GAS, E. WITHDRAWING FROM THE REGENERATION ZNE EFFLUENT GASHAVING A LOW CONTENT OF CARBON MONOXIDE, AND F. WITHDRAWNING FRON THEREGENERATION ZONE REGENERATED CATALYST PARTICLES HAVING A CONTENT OFRESIDUAL COKE FOR PASSAGE TO SAID REACTION ZONE
 9. A cyclic, continuousprocess for fluid catalytic cracking of petroleum hydrocarbons andcatalyst regeneration, wherein active, fluidizable cracking conversioncatalyst particles become spent while cracking a petroleum hydrocarbonfeedstock within a cracking reaction zone, spent catalyst particlescontaining coke are continuously withdrawn from the reaction zone andstripped in an inert gas stream, stripped spent catalyst particles arethereafter reactivated by burning coke therefrom in a fluidizedregeneration zone having a lower dense-phase section and an upperdilute-phase section, maintained at a regeneration temperaturesufficiently high to effect substantially complete burning of coke, andhot regenerated cracking catalyst particles are recycled to saidcracking reaction zone for use in said fluid catalytic cracking,comprising the steps of: a. introducing spent cracking catalystparticles, after stripping of residual volatile petroleum material, intoa lower dense-phase section of a fluidized regeneration zone containedwithin a regeneration vessel and maintained at regeneration temperature;b. introducing into the lower section of said regeneration zone anoxygen-containing regeneration gas stream in an amount in excess of thatrequired for complete combustion of the coke contained in the spentCatalyst particles and at an upward velocity sufficiently high to effectfluidization of said cracking catalyst particles; c. burning coke fromthe spent cracking catalyst particles in contact with saidoxygen-containing regeneration gas stream in said lower section of saidregeneration zone at said regeneration temperature while maintainingsaid catalyst particles in a dense-phase fluidized state by the upwardflow of said oxygen-containing gas stream, to provide a mixturecomprising fluidized regenerated cracking catalyst particles, togetherwith oxygen, carbon monoxide and carbon dioxide; d. substantiallycompleting the combustion of carbon monoxide in said regeneration gasstream to carbon dioxide in an upper dilute-phase section of saidregeneration zone at a temperature sufficiently high to supportcombustion of carbon monoxide; e. circulating fluidized regeneratedcracking catalyst particles upwardly from said lower section into saidupper section in an amount sufficient to absorb a major portion of theheat of combustion liberated by said combustion of carbon monoxide; f.absorbing said major portion of the heat of combustion of carbonmonoxide in said circulated fluidized regenerated cracking catalystparticles in direct heat-exchange contact in said upper section withsaid regeneration gas stream; g. separating a spent regeneration gasstream, containing carbon dioxide, excess oxygen and any unconvertedcarbon monoxide, from entrained catalyst particles and discharging thespent regeneration gas stream from the regeneration vessel; h.withdrawing regenerated cracking catalyst particles, substantially freeof coke and conserving the absorbed heat of combustion of said carbonmonoxide, from said regeneration zone and introducing said withdrawnregenerated cracking catalyst particles into the cracking reaction zone;and i. cracking a petroleum hydrocarbon feedstock with said regeneratedcracking catalyst particles in said cracking reaction zone underfluidizing conditions.
 10. The process of claim 9 wherein the combustionof carbon monoxide is substantially completed by controlling thetemperature in the upper section of the regeneration zone at a levelhigher than that maintained in the lower section of the regenerationzone, while sustaining the combustion of carbon monoxide with oxygen, atleast in part by adjusting the rate of curculation of regeneratedcracking catalyst particles from the lower section of the regenerationzone.
 11. The process of claim 9 wherein the oxygen-containingregeneration gas stream comprises air or oxygen-enriched air, flowingupwardly to provide fluidization of the lower dense-phase section of theregeneration zone, the regeneration temperature within the lower sectionof the regeneration zone is maintained within the range from about 1150*to about 1400*F., and the temperature within the upper section of theregeneration zone is maintained within the range from about 1200* toabout 1500*F.
 12. The process of claim 9 wherein the cracking catalystparticles comprise silica and alumina together with crystallinealuminosilicate.
 13. The process of claim 9 wherein the crackingreaction zone is a fluidized catalytic cracking reaction zone, suppliedwith petroleum cracking catalyst consisting essentially of 35-89 wt. %silica, 10-50 wt. % alumina and 1-15 wt. % crystalline aluminosilicate.14. The process of claim 9 wherein the regenerated cracking catalystparticles contain no more than about 0.05 wt. % coke and the spentregeneration gas stream contains no more than about 0.2 vol. % carbonmonoxide.
 15. The process of claim 9 wherein additional regeneratedcracking catalyst particles are circulated upwardly from the lowerdense-phase section of the regeneration zone into the upper section ofthe regeneration zone and dispersed within said upper section, in anamount sufficient to absorb substantially all of the evolVed heat ofcombustion and in response to the temperature of the dilute-phase zone.16. The process of claim 9 wherein at least about 80% of the evolvedheat of combustion of carbon monoxide is absorbed in the regeneratedcracking catalyst particles and transferred therein to the crackingreaction zone.
 17. The process of claim 9 wherein the burning of carbonmonoxide within the upper section of the regeneration zone initiated byburning sufficient torch oil within the dense-phase zone, whileadditionally introducing to said zone sufficient oxygen-containing gasto afford complete combustion of the torch oil, to provide a partiallyspent regeneration gas passing upwardly into said upper section at atemperature sufficiently high to sustain combustion of carbon monoxide,and thereafter ceasing the combustion of torch oil.
 18. The process ofclaim 9 wherein the burning of carbon monoxide within the upper sectionof the regeneration zone is initiated by momentary actuation of aspark-ignition means situated within and near the bottom of said uppersection, and thereafter ceasing the spark ignition.
 19. The process ofclaim 9 wherein the withdrawn regenerated cracking catalyst particlesare introduced into the cracking reaction zone at a temperature of atleast about 1,200*F.
 20. The process of claim 9 wherein the regeneratedcracking catalyst particles are returned to the cracking reaction zoneat substantially the temperature maintained in the lower dense-phasesection of the regeneration zone.
 21. The process of claim 9 wherein thecracking reaction zone is contained within a cracking reaction vessel ofthe transport type.
 22. The process of claim 9 wherein the cracking ofpetroleum hydrocarbon feedstock with regenerated cracking catalystparticles is effected in said cracking reaction zone under fluidizingconditions providing a cracking reaction time within the range fromabout 3 to about 10 seconds.
 23. A cyclic, continuous process for fluidcatalytic cracking of petroleum hydrocarbons and catalyst regeneration,wherein coke is burned from spent cracking catalyst particles in contactwith an excess of an oxygen-containing regeneration gas stream in afluidized dense-phase lower section of a regeneration zone and carbonmonoxide from said burning of coke is further burned to carbon dioxidein a dilute-phase upper section of said regeneration zone in contactwith sufficient catalyst particles to absorb most of the heat ofcombustion of said carbon monoxide, comprising the step of circulatingadditional catalyst particles into the upper section of the regenerationzone through an eductor tube situated within the regenerator vessel,said eductor tube extending substantially vertically from near thebottom of the dense-phase lower section to near the top of thedilute-phase upper section of the regeneration zone and terminating in adistributing head, the eduction of catalyst being effected with a jetstream of a gas directed upwardly into a bottom section of the eductortube, whereby the additional catalyst particles are lifted and dispersedsubstantially uniformly into a top portion of the upper section of theregeneration zone.
 24. The process of claim 9 wherein spent catalystparticles and the oxygen-containing gas are introduced separately into abottom section of the lower dense-phase section of the regeneration zoneand regenerated catalyst particles are withdrawn from a top section ofthe lower dense-phase section of the regeneration zone.
 25. The processof claim 9 wherein spent catalyst particles are first contacted with anexcess of an oxygen-containing regeneration gas in the lower dense-phasesection of the regeneration zone maintained at a temperature within therange from about 1,150* to about 1,400*F., and carbon monoxide isthereafter substantially completely burned to carbon dioxide within theupper dilute-phase section of the regeneration zone, at a temperaturemaintained within the range from about 1,200* to about 1,450*F.
 26. Theprocess of claim 25 wherein regenerated catalyst particles are withdrawnfrom the regeneration zone at a point near the top of the lowerdense-phase section of the regeneration zone and at a temperature ofabout 1,250*F.
 27. A cyclic, continuous process for fluid catalyticcracking of petroleum feedstock and catalyst regeneration, comprisingthe steps of: a. continuously feeding petroleum feedstock andregenerated fluidizable cracking catalyst particles, said catalystparticles being at a temperature of at least about 1,200*F., to a bottomsection of a fluid catalytic cracking reaction vessel in weightproportions selected to provide a catalyst-oil ration within the rangefrom about 2 to about 10; b. mixing the fluidizable cracking catalystparticles with the petroleum feedstock in said bottom section of thecracking reaction vessel, whereby the petroleum feedstock issubstantially completely vaporized at a mixing temperature of about1000*F. to provide a fluidized mixture of catalyst particles andpetroleum vapors; c. passing the fluidized mixture of catalyst particlesand petroleum vapors upwardly through the cracking reaction vessel at afluidizing velocity within the range from about 20 to about 60 feet persecond, whereby the cracking reaction is effected and the crackingreaction time is controlled within the range from about 3 to about 10seconds; d. continuously withdrawing a fluidized mixture of spentcatalyst particles having carbonaceous material deposited thereon andpetroleum vapors, including cracked petroleum vapor products, from a topsection of the cracking reaction vessel at a temperature of about950*F., rapidly separating said spent cracking catalyst particles fromsaid petroleum vapors, including cracked petroleum vapor products, andstripping said separated spent catalyst particles in an inert gasatmosphere at a stripping temperature of about 950*F.; e. continuouslyfeeding stripped spent cracking catalyst particles into a lower sectionof a fluidized catalyst regeneration zone, contained within a catalystregeneration vessel, together with an oxygen-containing regeneration gasin excess over the amount required for the complete combustion of thecarbonaceous material deposited upon the spent cracking catalystparticles, said gas flowing at a fluidizing velocity upwardly throughthe regeneration zone, said fluidizing velocity being within the rangefrom about 0.5 to about 3 feet/second; f. burning a major portion of thecarbonaceous material from the spent cracking catalyst particles withinthe lower section of the fluidized catalyst regeneration zone at atemperature maintained within the range from about 1150* to about1400*F., to provide a partially spent regeneration gas containing carbonmonoxide; g. burning substantially all of the remaining carbonaceousmaterial from the catalyst particles in the presence of the partiallyspent regeneration gas within an upper section of the fluidized catalystregeneration zone at a temperature maintained within the range fromabout 1,200* to about 1, 450*F.; h. simultaneously burning substantiallyall of the carbon monoxide contained in the partially spent regenerationgas within the upper section of the fluidized catalyst regeneration zoneat a temperature within the range from about 1,200* to about 1,450*F.;i. circulating fluidized regenerated cracking catalyst particlesupwardly from said lower section into said upper section in an amountsufficient to absorb at least about 80% of the heat of combustionliberated by said burning of carbon monoxide; j. absorbing said majorportion of the heat of combustion of carbon monoxide in said circulatedfluidized regenerated cracking catalyst particles in directheat-exchange contact in saiD upper section with said regeneration gasstream; k. discharging substantially spent regeneration gas, containingno more than about 2000 ppm carbon monoxide together with from about 1.0to about 3.0 vol. % oxygen, upwardly from the fluidized regenerationzone; l. withdrawing regenerated fluidizable cracking catalystparticles, containing no more than about 0.05 wt. % carbonaceousmaterial, from the catalyst regeneration zone at a temperature of atleast 1,200*F.; and m. returning said regenerated fluidizable crackingcatalyst particles, conserving at least 80% of the heat of combustion ofcarbon monoxide, at said temperature of at least about 1,200*F. to thebottom section of the fluid catalytic cracking reaction vessel.
 28. Theprocess of claim 27 wherein the fluid catalytic cracking reaction vesselis of the transport type.
 29. The process of claim 27 wherein thecracking reaction time is controlled within the range from about 3 toabout 7 seconds.